Technical Abstract:
Ichthyophthirius multifiliis (Ich) is one of the severe fish parasites that causes high mortality in both farmed and wild fish. Fish surviving Ich infections develop an immune response against parasite re-infection. This study evaluated cutaneous immunity against Ich in channel catfish. Using tissue culture technique, cutaneous antibodies were collected from the culture fluid of excised skin from fish immune to Ich. Cutaneous antibodies in immune culture fluid immobilized theronts, and the treatment of theronts with the immune culture fluid greatly reduced the attachment of theronts in excised tissues compared to those treated with the culture fluid from naive fish. In vivo, fewer fish were infected and the infection density was less for fish exposed to theronts treated with immune culture fluid. Cutaneous antibodies against Ich were detected in water taken from tanks containing immune fish. The immune fish cohabiting with non-immune fish provided partial protection to non-immune fish against Ich. Results of this study demonstrated that cutaneous immunity of channel catfish was involved in the protection against Ich invasion.